Where is it?

M40 junction 10, where the A43 splits off towards Northampton. This is one of the waypoints on the main freight route from Southampton to the north east.

The junction has been rebuilt since it was first listed in Bad Junctions. The description below was written about the previous layout, which ceased to operate in 2016.

What's wrong with it?

When the A43 between the M40 and M1 was upgraded to dual carriageway recently, this junction was updated too. It was built in 1991 as a regular two-roundabout dumbbell junction, but the improvements produced this. Amongst other things, it takes up more land than the previous junction, makes access in almost any direction difficult, and marginalises the most popular movement between M40 south and the A43. The previous set of four straight sliproads have been replaced by five sharply curved, narrow ones.

But what is most shocking about this junction is that at the northernmost roundabout, traffic from the A43 onto the M40 crosses traffic from the M40 north to the A43 — leaving north-eastbound traffic queuing northbound around two roundabouts and back onto the M40 northbound carriageway, even outside busy periods. It's such a stunningly shortsighted and dangerous mistake that it leaves me completely lost for words to describe how awful this new layout is.

Why is it wrong?

Well, here's the thing: it's hard to see any justification whatsoever for this layout. It's not smoother, it's not an improvement in width or speed of sliproads (in fact, lorries are now prone to tipping over on the sliproads), it doesn't make access to the services any easier... it makes, in short, no positive changes at all to the junction. How on earth did this design make it off the drawing board?

What would be better?

The most immediate solution would be to block the northernmost entry slip road to the M40 southbound, so A43 traffic no longer crosses at the northern roundabout. This would prevent almost all of the congestion at this junction. After that, I don't know. Maybe we could hunt down whoever designed this shameful mess.

Update: traffic lights have now been installed — no, not on the whole junction, just on the approach from the A43 south-westbound. Presumably when traffic gets bad enough northbound, these will act as 'ramp metering' — allowing bursts of traffic off the A43 southbound, creating gaps in the flow that will give northbound traffic a chance to get through.

There is also a new 50mph limit applying to the whole junction. This will make things much safer as one of the major problems it suffers is people tearing round those three queue-free roundabouts at dangerously high speeds.

Right to reply

I notice you have updated the page to reflect recent developments, but these haven't helped a great deal. The junction was closed again [a few weeks later] after yet another HGV fell over negotiating the roundabouts.

Now the lights have been installed on the southbound A43 the junction is much worse. Not only does Northampton-bound traffic exiting the M40 queue, but now at peak times the southbound does too, all the way back to RAF Croughton some 2-3 miles away! Why don't we all just get together and hire some diggers to re-open the old southbound slip road?! I hate this junction...

The only improvement I can see with the new layout is that A43 to M40 (northbound) traffic no longer conflicts with M40 (northbound) to A43 traffic - but is that really an issue? Certainly not a big enough one to rebuild an entire junction, I would submit.

Surely the solution to most of the problems here is obvious - connect the south-most of the 2 southbound on-slips to the roundabout, and not just the service area. Then close the curved southbound on-slip to the north. That immediately removes the main traffic conflict.

If you're feeling really energetic, re-instate the straight off-slip as well, which means you can remove the northern of the 3 roundabouts and keep the curved off-slip as a diverge for A43-bound traffic only. If that were topped off with a new off-slip for the services sited south of the junction, you remove the other major traffic conflict. The sad thing is that the fire at the services gave the HA and the Services operator a good chance to do something useful - but did they?

I can see the pigs soaring high above me on any of the above happening...

Some time before they were installed, I was on my way from Oxford to Northampton, and having heard of an accident that had closed the M40 at this junction, I travelled north on the B430.

However, it was the southbound M40 that was closed one junction further north, so there was no traffic leaving the motorway at this junction. That gave the A43 southbound traffic free access to the roundabout, as there was no traffic to give way to. Consequently, both M40 and B430 northbound on to the A43 joined forces at the M40 northbound exit roundabout, and was faced with the traffic leaving the A43 to join M40 south, where it had right of way.

I am puzzled by the layout of this junction. Who thought that the present curious layout, with two slip roads both providing access to the M40 southbound, was an improvement over what was there before? And why?

Combined with the A43 to M40 dual carriageway north of Oxford, this is the nightmare part of our journey from the west country to Kettering. I often use the old road via Weston-in-the-Green and country lanes near Fritwell to avoid it.

They have finally seen sense! I used to use this junction a lot driving between Reading and Nottingham and like everyone else was totally mystified by the 'improvements'.

However, I noticed on the current Road Schemes page that they have started work on closing the current southbound M40 slip road, and allowing access to the sliproad from the services. I wonder how much the original improvement scheme cost? Coupled with the cost of the new scheme that seems a lot of cash to make what will eventually be very little change (other than the hideous bendy slip road onto the Northbound M40 - although at least that serves the purpose of preventing northbound M40 traffic from crossing traffic leaving the M40).

What is the problem? The J10 M40/A43 'improvements' were designed to fail, and they have, spectacularly!

Now, at last, some of the idiocy is being reversed on the east side to remove one of the 'crossovers' - when will they do the same on the west side and restore the original northbound M40 access slip road?

I do remember once when I was at a friends house, who used to work in the Department for Transport, and their Midlands planning division. I was at his house and I noticed a file on his desk which was titled 'A43 Expressway - Grade Separation M40 to M1'. Whilst he was out of the room, I took a peek, I just couldn't help it! But from the brief glance I got it seems that the improvements made at M40 J10 and M1 J15A were only temporary, as the whole of the A43 was envisaged to be upgraded to a free flowing, fully grade separated expressway from the M40 to M1. I remember a date of summer 2014 being given as the date of completion of the new expressway. However as that date has passed I can only assume that the grand plans for the A43 and this junction were permanently scrapped long ago.

I'm so pleased to see that the madness of this junction has been recognised on your site. I have been using it almost daily for the past 16 years and hell on earth hardly covers it. You've said it all here but I would dearly love to know what bunch of numpties were responsible for the design. The cost to all of us in wasted time and wasted fuel must be astronomical.

Passing through here last month I was surprised to see some roadworks. Looks like the very solution you proposed on here - closing the northernmost slip onto the southbound M40 and preventing the two streams of traffic from crossing - is what's being built. Hooray!

Perhaps it is too early to judge but so far it has been bad, bad, bad. As someone who uses the B430 it usually did not take much time to get past the M40 junction once past Baynards Green. Not now with EVERYONE heading into two sets of traffic lights and the busiest southbound traffic immediately going from two lanes to one. I hate it.

Drove through here last Saturday evening (northbound, from M40 to A43) and found it has changed - as per comments from Richard Wale in February and Marcus M.

First roundabout (west of M40) is much the same.
Second roundabout now has a slip-lane round the left; I think it's just been done with paint, no new construction.
Third roundabout is now just three-way: there is NO slip-road to M40 south here. This removes one of the major conflicts.

Southbound traffic from A43 to M40 now has to bear left at this northern roundabout, and left again at the second roundabout. This must mean that there is a direct route from there to the M40 south (once again), without having to pass through the service area.

Throw in some traffic lights (I can't remember exactly where) and it's a great improvement. But of course an autumn evening is not a busy time.

I was glad to see that this junction was "fixed" earlier this year, eliminating the problems for northbound traffic, by returning to something close to the original layout. But this afternoon there was a two-mile tailback of southbound traffic on the A43, waiting to join a busy but flowing M40, held up, as far as I could tell, only by the new traffic lights. So they still have not got it right. More thought needed.

It isn't fixed, and neither is the M40-A34 junction at Wendlebury, which regularly causes queues back miles northbound from Oxford and southbound on the M40. The whole thing was misconceived, and the A34 - M40 - A43 route, hugely popular with freight from the coast heading for the M1 at Northampton should have been made free-flowing, merging into and out of a 4 lane stretch of the M40 between the two junctions.